Lecture_7b-Ross

Lecture_7b-Ross - Elec 300u Digital Modulation (Part II),...

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Unformatted text preview: Elec 300u Digital Modulation (Part II), Slide 1 Digital Modulation-2 • Impact of filtering on intersymbol interference (ISI) • Receiver noise vs. ISI • Concept of Raised Cosine Filter Some content taken with permission from material developed for the course EECS6.02 by C. Sodini, M. Perrot and H. Balakrishnan Digital Modulation • Digital modulation operates by sending discrete valued symbols through an analog communication channel- R e c e i v e r m u s t s a m p l e signals at the appropriate time every symbol period to maximize the probability of an accurate decision- Receiver matches sample values to corresponding symbols based on decision regions t 3 1-1-3 Baseband input x x LPF t Received signal channel 2cos(2 π f o t) 2cos(2 π f o t) sample/ slice 3 1-1-3 Eye Diagram – Shows transition behavior between symbols – Intersymbol interference (ISI) causes closing of eye – Also show sensitivity to sampling times Slicing levels Sampling times time 3 1-1-3 Symbol period Band-limited transmission system • Want transmitted spectrum with minimal bandwidth – Wireless communication channels are a shared resource • Issue : sharply changing digital waveforms lead to a wide bandwidth spectrum t x(t) T A-T Rectangular pulse Sinc freq spectrum ( Pros : no interference during the sampling time of other pulses) ( Cons : unbounded frequency response renders it unsuitable for band-limited transmissions) ransmitted spectrum of sharply changing waveforms t 3 1-1-3 Baseband Input t P(t) T * t = Transmit filter LPF Impulse train x 2cos(2 π f o t) Impact of Receiver Noise...
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This note was uploaded on 01/28/2011 for the course ELEC 300U taught by Professor Rossmurchandaminebermak during the Fall '08 term at HKUST.

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Lecture_7b-Ross - Elec 300u Digital Modulation (Part II),...

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